Hydraulic trip and reset relay



Feb. 6, 1968 J. B. WAGNER 3,367,369

HYDRAULIC TRIP AND RESET RELAY Filed Dec. 27, 1965 CONSTANT HYDRAULIC PRESSURE SOURCE PRESSURE RESPONSIVE DEVICE VARIABLE HYDRAULlC PRESSURE SOURCE INVENTOR JAMES B. WAGNER,

HIS ATTORNEY.

United States Patent Office 3,367,369 Patented Feb. 6, 1968 3,367,369 HYDRAULIC TRIP AND RESET RELAY James B. Wagner, Lynnfield, Mass., assignor to General Electric Company, a corporation of New York Filed Dec. 27, 1965, Ser. No. 516,261 3 Claims. (Cl. 137-625.66)

ABSTRACT OF THE DISCLOSURE A hydraulic relay has a movable piston controlling a pilot valve. The piston includes a restricted passage which is controlled by piston movement to give positive tripping and resetting at two different pressure levels.

This invention relates to hydraulic relays of the type which control the flow of a hydraulic fluid, in response to variations in pressure of a second hydraulic fluid. More particularly, the invention relates to such a relay which positively trips and resets at two separate selected pressure levels respectively of a variable hydraulic pressure source to eifect off-on control of another hydraulic fluid.

It is sometimes necessary and desirable to control the flow of a hydraulic fluid to a pressure responsive device in response to pressure variations in a second fluid, where the controlling relay will provide positive tripping at one selected pressure level and very rapid and positive resetting at a selected higher pressure level. An example of a system where the described relay is useful is found in a steam turbine control system. There it is desired that low bearing pressure will actuate a device to shut down the turbine, but when the bearing pressure is restored to a higher level the relay will reset and restore turbine operation.

Known systems using mechanical latches or springs are slow acting and not always reliable, often requiring calibration. More sensitive devices using pressure diaphragms may trip inadvertently upon momentary fluctuation of pressure which is only temporary. Also the tripping of some prior devices may not be of a positive nature, i.e., there is the possibility of hunting or cycling near the trip or reset pressures.

Accordingly, one object of the present invention is to provide an improved hydraulic relay for positive tripping and resetting response to a variable hydraulic pressure source.

Another object of the invention is to provide an improved hydraulic relay employing all hydraulically balanced elements without springs or other parts to get out of adjustment and requiring no calibration.

Still another object of the invention is to provide a hydraulic relay with snap action for tripping and resetting at two different selectable pressure levels, which is relatively insensitive to temporary pressure fluctuations.

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. The invention, however, both as to organization and method of practice, together with further objects and advantages thereof, may best be understood by reference to the following descrip tion taken in connection with the accompanying drawing, in which the single figure of the drawing is a sectional detailed view of the hydraulic relay in its normal untripped position.

Briefly stated, the invention is practiced by employing a relay piston biased with a constant force by a hydraulically loaded pilot valve. A pair of orifices, one supplying the relay piston chamber from a variable pressure source, and one controlling evacuation of the chamber, serve to determine the position of the relay piston and hence of the pilot valve. 1

Referring now to the drawing which shows the hydraulic relay in its normal untripped position, the relay has a pilot valve housing 1 connected to a relay piston housing 2. Pilot valve housing 1 is provided with a cylindrical bore 3 in which is slidably disposed a pilot valve member 4 having control lands 5, 6. Pilot valve 4 controls the access of fluid pressure from a substantially constant hydraulic pressure source 7 to a pressure responsive device 8 by uncovering or blocking a supply port 9, a control port 10, and a discharge port 11.

Pilot valve 4 is biased toward the left with a constant force by means of a slidable biasing piston 12, the righthand end of which is exposed to the constant pressure hydraulic source by means of a conduit 13. A thrust pin 12a transmits force between piston 12 and pilot valve 4.

The lefthand end of pilot valve 4 is provided with an extension 14 which extends toward the relay piston housing 2 to contact one side of a relay piston 15 disposed therein. Therefore, the biasing force of piston 12 is transmitted through pilot valve 4 so as to constantly urge relay piston 15 to the left.

The righthandside of relay piston 15 communicates with a passage 16 which is open to drain as indicated on the drawing. The lefthand side of relay piston 15 is exposed to the pressure in a chamber 17 Within the relay piston housing 2. A slidable rod 18 extends through an end wall 2a of the housing to actuate an exterior switch 19 in accordance with the position of relay piston 15.

Relay piston chamber 17 is supplied with hydraulic fluid from a variable hydraulic pressure source 20 through a supply orifice 21. Flow out of chamber 17 is provided for by means of a second orifice 22 communicating with chamber 17 by means of a passage 23 which is formed in the extension rod 18. Passage 23 is always open to chamber 17 despite the position of piston 15, but the orifice 22 is blocked or open according to whether piston 15 is to the right or left respectively. When orifice 22 is open, fluid can escape through the orifice to drain conduit 24. It should be noted that orifice 22 in rod 18 is opened or closed at approximately the halfway point in the travel of relay piston 15. This provides the proper time constant for the relay as will be explained.

The operation of the hydraulic relay may now be described, with reference first to the untripped position shown in the drawing. The static pressure in chamber 17 to the left of the piston 15 is substantially the same as that of the variable hydraulic pressure source 20 which may be, for example, turbine bearing pressure running on the order of 25 p.s.i.g. The force to the right on piston 15 due to the pressure in chamber 17, is greater than that provided by biasing piston 12 to the left and the pilot valve 4 remains in the position shown, so that fluid from the constant hydraulic pressure source 7 is in communication with the pressure responsive device 8 through supply port 9 and control port 10.

Assuming that the pressure from source 20 begins to decrease, eventually the static pressure in chamber 17 will to approximately half its previous value, since fluid from pressure source 20 now flows through two flow constrictions in series, i.e., first through orifice 21 and then through orifice 22. Since the force on the lefthand side of piston 15 has substantially decreased, piston 15 will snap to the I left under the action of biasing piston 12. At the same time, pilot valve 4 moves to the left. Pilot valve land 5 now blocks the inlet port 9 and provides communication between control port 10 and discharge port 11 to dump hydraulic fluid from the pressure responsive device 8.

It is important to note that slight movement to the left of piston under temporary fluctuation of the variable pressure will not uncover orifice 22. Thus a slight delay is obtained, which is desirable, before positive trip action occurs.

Assuming now that the pressure from source again increases, it must increase to a higher value than that at which it tripped. This value must be such that the intermediate pressure in chamber 17 between the two orifices in series causes a force to exceed that of the constant biasing force provided by piston 12. When this happens the piston 15 begins to move to the right. Halfway through its travel, the orifice 22 is blocked, and pressure substantially doubles in chamber 17 causing relay piston 15 to snap to the right with positive action as before.

To summarize, relay tripping is caused by the decrease of a static pressure in chamber 17 supplied through a single orifice. Resetting is caused by increase in a dynamic intermediate pressure between two orifices in series. Transfer between the two modes of operation is determined by covering and uncovering of the orifice 22 as piston 15 moves.

The relative values of trip pressure and reset pressure are determined by the relationship of the selected sizes of orifices 21 and 22. The time constant is selected by proper'location of orifice 22 along the slidable rod 18.

Although the relative size of orifice 21 with respect to orifice 22 will vary with the application desired, the particular arrangement shown employs a diameter of 0.10" for orifice 21 and diameter of 0.12 for the orifice 22. Thus the effective area of orifice 22 is on the order of 144% of the effective area of orifice 21. With a constant hydraulic pressure source of 1600 p.s.i.g. and a diameter of 0.3125 inch for biasing piston 12 and a diameter of 4.50 inches for piston 15, the foregoing orifice sizes result in tripping of the relay piston 15 at 8 p.s.i.g. and resetting of piston 15 at 16 p.s.i.g.

While the relay illustrated employs separate relay piston, extension rod, pilot valve, and biasing piston members, it will be appreciated that these could be made as an integral piece so that the relay piston 15 and rod 18 be attached to one end of the pilot valve 4 and the biasing piston 12 would be formed as an extension on the other end of the pilot valve.

While there has been described herein the preferred embodiment of the invention, it will be understood that various other changes and modifications might be made. It is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What I claim is:

1. A hydraulic relay for controlling the flow of fluid from a first substantially constant pressure source to a pressure responsive device in response to variations in pressure from a second variable pressure source, compnsmg:

a relay housing defining first and second chambers at opposite ends thereof and also defining intermediate supply, discharge and control ports,

valve means slidably disposed in said housing having opposite large and small piston end portions arranged to slide in the first and second chambers respectively, said valve means also having intermediate lands controlling the flow of fluid through said intermediate ports,

first conduit means connecting said first pressure source to the first chamber and also to the supply port,

second conduit means connecting said control port to said pressure responsive device,

third conduit means having a supply orifice therein connecting the second pressure source to the second chamber,

fourth conduit means defined within an extension member attached to the large piston end portion of the valve means so as to be movable therewith and having a discharge orifice therein, said fourth conduit having an inlet communicating with the second chamber and having an outlet which is arranged to be covered by a housing portion when the valve means is in a first position and opened to drain when the valve means is in a second position,

whereby full second source pressure opposes full first source pressure when the valve means is in the first position and whereby an intermediate pressure in the second chamber between the supply and discharge orifices opposes first source pressure when the valve means is in the second position.

2. The combination according to claim 1 wherein said fourth conduit means is so disposed in the extension member with relation to the housing portion, so that said outlet is ported and unported by the housing portion when the valve means is substantially midway between the first and second position, so that small movements of the valve means near the first or second positions will not block or unblock the fourth conduit means.

3. A hydraulic relay for controlling the flow of fiuid from a first substantially constant pressure source to a pressure responsive device in response to variations in pressure from a second variable relatively low pressure source, comprising:

a relay housing defining large and small piston chambers at opposite ends thereof and also defining an intermediate pilot valve chamber, said housing also defining intermediate supply, discharge and control ports connecting with the pilot valve chamber,

a relay piston slidably disposed in the large piston chamber and having an extension member attached thereto extending through a housing portion,

a pilot valve slidably disposed in the pilot valve chamber and having lands controlling the flow of fluid through said intermediate ports, said pilot valve being aligned to abut the relay piston,

a biasing piston slidably disposed in the small piston chamber and aligned to abut the pilot valve,

first conduit means connecting said first pressure source to the small piston chamber to cause the biasing piston to urge the pilot valve toward the relay piston,

second conduit means having a supply orifice therein connecting the second pressure source to the large piston chamber so as to cause the relay piston to urge the pilot valve toward the biasing piston,

third conduit means defined within said extension rod so as to be movable therewith, said third conduit means opening at one end into the large piston cham-' her on the first pressure source side of the relay piston, said third conduit having a discharge orifice therein with an outlet which is blocked by said housing portion when the relay piston is on a first position and opened to drain when the relay piston is 1n a second position,

whereby full pressure from the second source opposes full first source pressure when the relay piston is in the first position and whereby an intermediate pressure in the large piston chamber between the supply and discharge orifices opposes first source pressure when the relay piston is in the second position.

References Cited UNITED STATES PATENTS 2,775,982 1/1957 Canfield 137-62564 2,898,936 8/1959 Collins 137-62563 2,916,050 12/1959 Ruhl 37-625.68 2,979,080 4/1961 Hewitt 137625.68 2,993,511 7/1961 Johnson 137625.64 3,126,915 3/1964 Hunt 137-62564 XR 3,209,781 10/1965 Strader l37-625.68 XR 3,219,060 11/1965 Pearl et al. 137-625.66 XR 3,258,025 6/1966 Howland 137-625.64 XR HENRY T. KLINKSIEK, Primary Examiner. 

